Project Summary/Abstract Neuropeptides are one of the major signals that are used by neurons to modulate behavior and physiology, and neuropeptide receptors are important therapeutic targets for the treatment of disease. This proposal explores neuropeptide signaling in the nematode C. elegans in two parts. In the first part (Specific Aim 1), I propose a series of experiments that will elucidate the neural circuit regulated by vasotocin, a novel C. elegans ortholog of the mammalian neuropeptides vasopressin and oxytocin. These experiments aim to define the minimal components of a neuropeptidergic circuit that regulates behavior in a model organism. In the second part (Specific Aims 2 and 3), I describe the development of two new approaches for the cell-specific analysis of neuropeptide signaling in the worm. The first technique will enable the blockade of all neuropeptide production within a single cell (Specific Aim 2) and the second will enable the genome-wide profiling of neuropeptide translation within single neurons in the mature nervous system (Specific Aim 3). I further describe how I will apply these technologies to test hypotheses about two circuits that are believed to utilize neuropeptide signaling, but for which the specific neuropeptide mediators remain enigmatic: the regulation of thermotaxis by AFD neurons and the regulation of longevity by ASI neurons.